The present invention concerns a process of making a bobbin in the form of truncated conical member particularly for use in winding textile threads and/or ribbons, of a type formed by rolling layers of a paper or cardboard blank on a conical mandrel and adhesively securing the layers together; the aforementioned blank is obtained by cutting a web of paper or cardboard and rolling the blank to make the trunk of the cone to be formed.
Obviously, the present invention also involves the truncated cone bobbins which are obtained by such a procedure.
In the textile industry, hollow truncated cone bobbins are widely used for winding threads or ribbons. These conventional support cones are characterized by being formed in a wide variety of different sizes, weights and dimensions of their sides so that their resistance to lateral compression at their bottom ends as well as resistance to crimping along their base and tops will vary. The exterior surface of conventional cones can be formed to give the choice between a smooth surface or a corrugated surface which can facilitate the clinging of the textile threads to the cones. Also, the exterior surface can be provided with slits, grooves, and/or perforations and at least one niche to enable securing of the end of the thread or ribbon to the cone.
In FIGS. 1 and 2, attached, of the first set of drawings for the present application, there is shown a perspective view and a cross-section of a truncated support cone 1, of conventional form, of which the height is designated by h, the radius at any point M of the trunk of the cone is designated by r, and the thickness of the hollow cone is shown by e. FIGS. 3 and 4 illustrate the traditional process of manufacture of such truncated support cones 1.
The conventional process consists of movable web 3 of paper or cardboard which is moved in the direction shown by arrow 2 supplied from a roll which is not depicted. The web is cut to provide polygonal templates or blank elements 4, generally symmetrical in relation to a longitudinal axis 3' of the web shaped somewhat in the form of chevrons placed side by side and one after the other. In this manner, two principal cuts are made along lines 5 and 6 repeatedly as shown so as to create a blank in the shape of a chevron having lower and upper edges 17 and 18 as shown in FIG. 4.
The two cuts 5 and 6 follow two incipient cuts 9 and 10 to result in the severing of the lateral points 7 and 8 of the chevron, when the principal cuts 5 and 6 are made. The web from which the chevron is cut has previously been provided with a roughened surface along each of its longitudinal edges. One of the roughened surfaces is provided on the lower face of the web and extends all along zone 11 following cut 10. The other roughened surface is provided on the upper face of the web and extends through zone 12 below cut 9. The roughened surfaces extend inwardly from each edge of the web approximately 25% of the width of the web. The chevron-shaped blank which is thus formed is then rolled around a mandrel along line 10 as shown by arrow 13. The roughened areas have adhesive applied to them in zones 11 and 12 so as to secure the ends of the blank to the body of the cone provided as the result of the rolling of the chevron-shaped blank.
In other words, for each template or blank 4 obtained in web 3 after four successive cuts, respectively 5-6-9-10, and after roughening the external surface 11 where the template begins, and internal surface 12 where it ends, one proceeds successively to various other operations to obtain the desired truncated cone, namely:
First, gluing of the exterior surface of the blank to itself while simultaneously rolling the blank around the mandrel and also simultaneously trimming the base and the tip, for example, with two blades.
The item is then dried and formation of the bottoms effected such as a crimping of the base and/or the tip of the trunk of the cone 1. The exterior surface can then be roughened to permit a better grip of the textile threads, and the slit is cut at the base of the trunk of the cone for receiving the end of the thread to be wound on the cone.
According to the actual process, one sees that there is created substantial waste of material consisting of areas 7 and 8 and the hatched surfaces 15, 15', and 16 as shown in FIG. 4. The loss of material is about 40% of the original material of the web 3.
On the other hand, according to the traditional method of manufacture indicated above, one creates truncated cone supports of which the thickness e is constant, due to the fact that there are the same number of layers of material at the base as at the tip.
A support cone supports thread or the like by lateral compression, and in order to obtain equal resistance along the whole height of cone, the thickness of the conical support should be proportional to the diameter at any particular location.
In effect, the stress at a point M on the surface of cone 1 (FIG. 2) on which the force due to the rolling of the thread upon the cone is equally shared is proportional to the relation (p.times.r)/e in which p indicates the effective pressure.
Thus, the thickness e of the traditional cones being constant, greater stresses result at the base of the cone than at the upper end tip of the truncated cone 1 and, since at the same time, the lower end of the cone must have a thickness to resist maximum stress, which occurs at its base, a large quantity of waste material results in the upper end portions of the cone.
Finally, the machines currently used to manufacture such conventional truncated cone bobbins employ many mechanical movements, particularly the machine or machines which have the function of performing the four cuts in the web necessary for forming each blank, are slow in operation and consequently economically disadvantageous.
Therefore, it is the object of the present invention to provide a process of manufacture of bobbing in the form of truncated cone supports which permit a great reduction in the waste material and provide a maximum ratio of strength to weight while improving the speed and efficiency of production.